(1) Field of Invention
This invention relates to novel methods for preparing fluorinated organic compounds, and more particularly to methods of producing fluorinated olefins.
(2) Description of Related Art
Hydrofluorocarbons (HFC's), in particular hydrofluoroalkenes such tetrafluoropropenes, including particularly 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze)) have been disclosed to be effective refrigerants, fire extinguishants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), both of which potentially damage the Earth's ozone layer, HFCs do not contain chlorine and thus pose no threat to the ozone layer.
Several methods of preparing HFO-1234ze are known. For example, U.S. Pat. No. 6,124,510 discloses a process for preparing a product stream containing HFO-1234ze. The described process comprises the step of dehydrofluorination of HFC-245fa using either an alkaline solution of a strong base (such as an aqueous or alcoholic solution of potassium hydroxide), or a chromium-based catalyst, preferably in a vapor phase. The composition produced by the examples of the disclosed processes contains relatively large concentrations of the cis-isomer of HFO-1234ze. More specifically, the three examples disclosed in this patent produce compositions containing both trans-HFO-1234ze and cis-HFO-1234ze, with amount of cis-isomer in the composition ranging from 17.7% to 23.9%. As a result, the methods disclosed in U.S. Pat. No. 6,124,510, as described in the examples thereof, produce product compositions having a relatively low concentration of trans-HFO-1234ze, namely, concentrations ranging from 74% to 80.5%.
Applicants have come to appreciate the need for and have developed processes for producing, preferably in an efficient and cost effective manner, compositions containing HFO-1234ze having relatively high concentrations of trans-isomer. In one aspect, applicants have determined that known processes are generally not economical relative to their product yield, particularly due to the formation of significant amounts of the undesired cis-isomer in the product stream of such know processes.